Mesenchymal stromal cells with chimaeric antigen receptors for enhanced immunosuppression.

Allogeneic mesenchymal stromal cells (MSCs) are a safe treatment option for many disorders of the immune system. However, clinical trials using MSCs have shown inconsistent therapeutic efficacy, mostly owing to MSCs providing insufficient immunosuppression in target tissues. Here we show that antigen-specific immunosuppression can be enhanced by genetically modifying MSCs with chimaeric antigen receptors (CARs), as we show for E-cadherin-targeted CAR-MSCs for the treatment of graft-versus-host disease in mice. CAR-MSCs led to superior T-cell suppression and localization to E-cadherin+ colonic cells, ameliorating the animals' symptoms and survival rates. On antigen-specific stimulation, CAR-MSCs upregulated the expression of immunosuppressive genes and receptors for T-cell inhibition as well as the production of immunosuppressive cytokines while maintaining their stem cell phenotype and safety profile in the animal models. CAR-MSCs may represent a widely applicable therapeutic technology for enhancing immunosuppression.

AXL Inhibition Improves the Antitumor Activity of Chimeric Antigen Receptor T Cells.

The receptor tyrosine kinase AXL is a member of the TYRO3, AXL, and proto-oncogene tyrosine-protein kinase MER family and plays pleiotropic roles in cancer progression. AXL is expressed in immunosuppressive cells, which contributes to decreased efficacy of immunotherapy. Therefore, we hypothesized that AXL inhibition could serve as a strategy to overcome resistance to chimeric antigen receptor T (CAR T)-cell therapy. To test this, we determined the impact of AXL inhibition on CD19-targeted CAR T (CART19)-cell functions. Our results demonstrate that T cells and CAR T cells express high levels of AXL. Specifically, higher levels of AXL on activated Th2 CAR T cells and M2-polarized macrophages were observed. AXL inhibition with small molecules or via genetic disruption in T cells demonstrated selective inhibition of Th2 CAR T cells, reduction of Th2 cytokines, reversal of CAR T-cell inhibition, and promotion of CAR T-cell effector functions. AXL inhibition is a novel strategy to enhance CAR T-cell functions through two independent, but complementary, mechanisms: targeting Th2 cells and reversing myeloid-induced CAR T-cell inhibition through selective targeting of M2-polarized macrophages.

GM-CSF disruption in CART cells modulates T cell activation and enhances CART cell anti-tumor activity.

Inhibitory myeloid cells and their cytokines play critical roles in limiting chimeric antigen receptor T (CART) cell therapy by contributing to the development of toxicities and resistance following infusion. We have previously shown that neutralization of granulocyte-macrophage colony-stimulating factor (GM-CSF) prevents these toxicities and enhances CART cell functions by inhibiting myeloid cell activation. In this report, we study the direct impact of GM-CSF disruption during the production of CD19-directed CART cells on their effector functions, independent of GM-CSF modulation of myeloid cells. In this study, we show that antigen-specific activation of GM-CSFKO CART19 cells consistently displayed reduced early activation, enhanced proliferation, and improved anti-tumor activity in a xenograft model for relapsed B cell malignancies. Activated CART19 cells significantly upregulate GM-CSF receptors. However, the interaction between GM-CSF and its upregulated receptors on CART cells was not the predominant mechanism of this activation phenotype. GM-CSFKO CART19 cell had reduced BH3 interacting-domain death agonist (Bid), suggesting an interaction between GM-CSF and intrinsic apoptosis pathways. In conclusion, our study demonstrates that CRISPR/Cas9-mediated GM-CSF knockout in CART cells directly ameliorates CART cell early activation and enhances anti-tumor activity in preclinical models.

Dynamic Imaging of Chimeric Antigen Receptor T Cells with [18F]Tetrafluoroborate Positron Emission Tomography/Computed Tomography.

T cells genetically engineered to express chimeric antigen receptors (CAR) have shown unprecedented results in pivotal clinical trials for patients with B cell malignancies or multiple myeloma (MM). However, numerous obstacles limit the efficacy and prohibit the widespread use of CAR T cell therapies due to poor trafficking and infiltration into tumor sites as well as lack of persistence in vivo. Moreover, life-threatening toxicities, such as cytokine release syndrome or neurotoxicity, are major concerns. Efficient and sensitive imaging and tracking of CAR T cells enables the evaluation of T cell trafficking, expansion, and in vivo characterization and allows the development of strategies to overcome the current limitations of CAR T cell therapy. This paper describes the methodology for incorporating the sodium iodide symporter (NIS) in CAR T cells and for CAR T cell imaging using [18F]tetrafluoroborate-positron emission tomography ([18F]TFB-PET) in preclinical models. The methods described in this protocol can be applied to other CAR constructs and target genes in addition to the ones used for this study.

Challenges of chimeric antigen receptor T-cell therapy in chronic lymphocytic leukemia: lessons learned.

Development of chimeric antigen receptor T cell (CART) therapy has led to an unprecedented success against B-cell leukemia and lymphoma and resulted in U.S. Food and Drug Administration-approved treatment protocols. Despite the initial clinical response in B cell-related malignancies, high relapse rates suggest that much work is needed to uncover mechanisms of resistance. In chronic lymphocytic leukemia (CLL), the durable activity of CAR T-cells is limited, and CAR T-cell therapy success is lower than in other malignancies. T cells from these patients are vulnerable to a state of dysfunction because of stresses including chronic infection, rapid cell cycle on antigen recognition, immunosuppressive tumor microenvironment, and cancer-related treatments. T cells are also introduced to additional stresses when cultured ex vivo during the CAR T-cell manufacturing process. All these factors contribute to the limited regenerative capacity of T cells, which can lead to CAR T-cell treatment failure. In this article, we review the challenges of CAR T-cell therapy in patients with CLL and discuss potential strategies to overcome these challenges.

Targeting cancer-associated fibroblasts in the bone marrow prevents resistance to CART-cell therapy in multiple myeloma.

Pivotal clinical trials of B-cell maturation antigen-targeted chimeric antigen receptor T (CART)-cell therapy in patients with relapsed/refractory multiple myeloma (MM) resulted in remarkable initial responses, which led to a recent US Food and Drug Administration approval. Despite the success of this therapy, durable remissions continue to be low, and the predominant mechanism of resistance is loss of CART cells and inhibition by the tumor microenvironment (TME). MM is characterized by an immunosuppressive TME with an abundance of cancer-associated fibroblasts (CAFs). Using MM models, we studied the impact of CAFs on CART-cell efficacy and developed strategies to overcome CART-cell inhibition. We showed that CAFs inhibit CART-cell antitumor activity and promote MM progression. CAFs express molecules such as fibroblast activation protein and signaling lymphocyte activation molecule family-7, which are attractive immunotherapy targets. To overcome CAF-induced CART-cell inhibition, CART cells were generated targeting both MM cells and CAFs. This dual-targeting CART-cell strategy significantly improved the effector functions of CART cells. We show for the first time that dual targeting of both malignant plasma cells and the CAFs within the TME is a novel strategy to overcome resistance to CART-cell therapy in MM.

Development of a Clinically Relevant Reporter for Chimeric Antigen Receptor T-cell Expansion, Trafficking, and Toxicity.

Although chimeric antigen receptor T (CART)-cell therapy has been successful in treating certain hematologic malignancies, wider adoption of CART-cell therapy is limited because of minimal activity in solid tumors and development of life-threatening toxicities, including cytokine release syndrome (CRS). There is a lack of a robust, clinically relevant imaging platform to monitor in vivo expansion and trafficking to tumor sites. To address this, we utilized the sodium iodide symporter (NIS) as a platform to image and track CART cells. We engineered CD19-directed and B-cell maturation antigen (BCMA)-directed CART cells to express NIS (NIS+CART19 and NIS+BCMA-CART, respectively) and tested the sensitivity of 18F-TFB-PET to detect trafficking and expansion in systemic and localized tumor models and in a CART-cell toxicity model. NIS+CART19 and NIS+BCMA-CART cells were generated through dual transduction with two vectors and demonstrated exclusive 125I uptake in vitro. 18F-TFB-PET detected NIS+CART cells in vivo to a sensitivity level of 40,000 cells. 18F-TFB-PET confirmed NIS+BCMA-CART-cell trafficking to the tumor sites in localized and systemic tumor models. In a xenograft model for CART-cell toxicity, 18F-TFB-PET revealed significant systemic uptake, correlating with CART-cell in vivo expansion, cytokine production, and development of CRS-associated clinical symptoms. NIS provides a sensitive, clinically applicable platform for CART-cell imaging with PET scan. 18F-TFB-PET detected CART-cell trafficking to tumor sites and in vivo expansion, correlating with the development of clinical and laboratory markers of CRS. These studies demonstrate a noninvasive, clinically relevant method to assess CART-cell functions in vivo.

Resistance to CART cell therapy: lessons learned from the treatment of hematological malignancies.

Chimeric antigen receptor T (CART) cell immunotherapy has yielded significant clinical success in treating certain hematological malignancies. However, despite high initial response rates, most patients eventually relapse. Resistance to CART cell therapy can stem from tumor cell mutations, T cell defects, and tumor microenvironment (TME) immunosuppression. Tumor cells can downregulate target antigen expression to evade CART cell detection or mutate death receptor pathways to resist CART cell cytotoxicity. Patient T cells can be intrinsically defective, and CART cells often undergo exhaustion. The TME is abundant with immunosuppressive cells and factors which contribute to suboptimal CART cell activity. Collectively, issues originating in tumor cells, T cells, and the TME present significant hurdles to long-term remission after CART cell therapy. Various strategies to combat CART cell resistance have shown promise in preclinical studies and early clinical trials and are crucial to achieving durable responses.

Leukemic extracellular vesicles induce chimeric antigen receptor T cell dysfunction in chronic lymphocytic leukemia.

Chimeric antigen receptor (CAR) T cell therapy has yielded unprecedented outcomes in some patients with hematological malignancies; however, inhibition by the tumor microenvironment has prevented the broader success of CART cell therapy. We used chronic lymphocytic leukemia (CLL) as a model to investigate the interactions between the tumor microenvironment and CART cells. CLL is characterized by an immunosuppressive microenvironment, an abundance of systemic extracellular vesicles (EVs), and a relatively lower durable response rate to CART cell therapy. In this study, we characterized plasma EVs from untreated CLL patients and identified their leukemic cell origin. CLL-derived EVs were able to induce a state of CART cell dysfunction characterized by phenotypical, functional, and transcriptional changes of exhaustion. We demonstrate that, specifically, PD-L1+ CLL-derived EVs induce CART cell exhaustion. In conclusion, we identify an important mechanism of CART cell exhaustion induced by EVs from CLL patients.

Using CRISPR/Cas9 to Knock Out GM-CSF in CAR-T Cells.

Chimeric antigen receptor T (CAR-T) cell therapy is a cutting edge and potentially revolutionary new treatment option for cancer. However, there are significant limitations to its widespread use in the treatment of cancer. These limitations include the development of unique toxicities such as cytokine release syndrome (CRS) and neurotoxicity (NT) and limited expansion, effector functions, and anti-tumor activity in solid tumors. One strategy to enhance CAR-T efficacy and/or control toxicities of CAR-T cells is to edit the genome of the CAR-T cells themselves during CAR-T cell manufacturing. Here, we describe the use of CRISPR/Cas9 gene editing in CAR-T cells via transduction with a lentiviral construct containing a guide RNA to granulocyte macrophage colony-stimulating factor (GM-CSF) and Cas9. As an example, we describe CRISPR/Cas9 mediated knockout of GM-CSF. We have shown that these GM-CSFk/o CAR-T cells effectively produce less GM-CSF while maintaining critical T cell function and result in enhanced anti-tumor activity in vivo compared to wild type CAR-T cells.

GM-CSF inhibition reduces cytokine release syndrome and neuroinflammation but enhances CAR-T cell function in xenografts.

Chimeric antigen receptor T (CAR-T) cell therapy is a new pillar in cancer therapeutics; however, its application is limited by the associated toxicities. These include cytokine release syndrome (CRS) and neurotoxicity. Although the IL-6R antagonist tocilizumab is approved for treatment of CRS, there is no approved treatment of neurotoxicity associated with CD19-targeted CAR-T (CART19) cell therapy. Recent data suggest that monocytes and macrophages contribute to the development of CRS and neurotoxicity after CAR-T cell therapy. Therefore, we investigated neutralizing granulocyte-macrophage colony-stimulating factor (GM-CSF) as a potential strategy to manage CART19 cell-associated toxicities. In this study, we show that GM-CSF neutralization with lenzilumab does not inhibit CART19 cell function in vitro or in vivo. Moreover, CART19 cell proliferation was enhanced and durable control of leukemic disease was maintained better in patient-derived xenografts after GM-CSF neutralization with lenzilumab. In a patient acute lymphoblastic leukemia xenograft model of CRS and neuroinflammation (NI), GM-CSF neutralization resulted in a reduction of myeloid and T cell infiltration in the central nervous system and a significant reduction in NI and prevention of CRS. Finally, we generated GM-CSF-deficient CART19 cells through CRISPR/Cas9 disruption of GM-CSF during CAR-T cell manufacturing. These GM-CSFk/o CAR-T cells maintained normal functions and had enhanced antitumor activity in vivo, as well as improved overall survival, compared with CART19 cells. Together, these studies illuminate a novel approach to abrogate NI and CRS through GM-CSF neutralization, which may potentially enhance CAR-T cell function. Phase 2 studies with lenzilumab in combination with CART19 cell therapy are planned.